Product and process for the production of aqueous gels



United States Patent PRODUCT AND PROCESS'FOR THE PRODUCTION OF AQUEOUSGELS No Drawing. Application February 12, 1958 Serial No. 714,672

Claims'priority, application Germany February 22, 1957 15 Claims. (Cl.99-131) 'This invention relates to a composition useful in thefiformation of aqueous gels containing partial amides of ,polyuronicacids and the corresponding process.

It is known that polyuronic acid esters may be reacted with liquidammonia to form the corresponding polyruronic acid amides. In thismanner it is possible to ob- (tain polyuronic acid amides in which aportion or all of the carboxyl groups originally present in thepolyuronic acid are transformed into amides. In addition to thecarbonamide groups, if the transformation is incomplete, the polyuronicacid amides contain varying quantities of carboxyl groups neutralizedwith ammonia and a small number of 'carboxylic acid ester groups. Thepresence "of these groups can be explained either by the fact that theesterification of the free polyuronic acids did not proceed tocompletion, and further that the amidation of the ester groups waslikewise incomplete, or that during the amidation of the ester groups asaponification of the carboxylic acid ester group too-k'place to a minordegree. Thus, by a choice of more or less completely e'sterifiedpolyuronicacids orby'a-choi'ce of suitable working conditions, it-ispossibleto'contro'l theproduction of preparations in which a varyingpercentage of the carboxyl groups originally present have beentransformed into amide-group's. If a high percentage of '.thecarboxylgroups originally present have been transformed into carb'o'namidegroups--for example, 80 to 90% of them' the products'so 'pr'oduc'edhayethe property bfswelling {in cold water Without, however, dissolvingtherein. When the water is heated, however, they dissolve and uponcooling of the solution formthermo-reversible aqueous ;gelsthat is, gelswhich can be liquefied by'heating the .same and subsequently transformedonce again into gels by cooling as often as desired, providedthesolutiondoes not contain substances which saponify the carbonamidegroups or which tend to degrade the carbohydrate structure of thepolyuronic acid amides. With a decreasing number of carbonamide groupsin the molecule and an increasing number of' neutralized carboxyl groupsin the molecule, the gel-forming properties of the polyuronic acidamides decrease; in other words, the products swell in col'dwater to anincreasing degree and. gels formed therewith become increasingly lesssolid, so that with a decreasing content of carboxylic acid amide groupsit is possible to observe a smooth transition from a stiff gel to ahighly viscous solution which no longer'con- "rains any gellingproperties at all.

An' object of our invention is'to improve gel forming properties ofthose partial amides of polyuronic acids which have a higher content ofcarboxyl groups and'to enhance gel-forming properties of those partialamides of polyuronic acids which have a low content of 'carboxyl groups.7

Another object of "our invention is to provide a composition of dryingredients which will bereadily soluble in watera'ndf wiiich will formheat-reversible gels after olutioninwater;

2,919,198 V Patented Dec. 1959 A-f-urther object of our invention is acomposition which is readily soluble incold water and which uponsolution sets into a heat-reversible aqueous gel.

We have found that amides of polyuronic acids which contain a largenumber of carbonamide groups (CQNR R and a lesser number of neutralizedcarboxyl groups (-C0OMe) can be" transformed into aqueous gelsespecially readily if they'are dissolved in water in the presence of asubstance which upon solution slowly forms anacid in water.

Partial-carboxylic acid amides which are primarily useful for thecomposition andrthe process of our invention are the amides of alginicacid, pectic acid or cellulose'glycolic acid. The production of thepartial alginic acid amides is described in ourcopending United States-applicationSer. No. 496,920, filed March 25-, 1955, now Patent#2,88l,16-1. These amides should contain from 0.5 to 1.5, preferablyfrom 0.6 to 1.0, acyl groups per uronic 'acid unit. About 50% to aboutof the acyl groups should be present in the form of carbonamide groups,whereas, the remaining acylgroups should be present substantially in;the form of neutralized carboxyl groups. l The cation of theseneutralized carboxyl groups is preferably-the ammonium ion, but productswhich contain the cations of mono-basic organic or inorganic bases mayalso be worked up with equal success.

Suitable non-acidic-reacting substances which form acids gradually .inthe presence of water are lactones of hydroxy acids and those acidanhydrides which likewise form. acids gradually in the presence of,water. Within the seriesof lactones, primarily the lactones of sugaracids, such as-gluc onic acid lactone or mannuronic acid lactone,areprefer-able. An example-of a useful acid anhydride is glycolic acidanhydride.

Tocarry out the process according to our invention, the, acid-formingsubstances .and the partial polyuronic acid amide's are dissolved inwaterasimultaneously or in any desired sequence. However, care should betaken that the acid amides are dissolved before significantquantities'of acid have beenformed. It is therefore advantageous tointroduce the partial polyuronic acid amides into the water prior to ortogether with the acid-forming substances. In general, a highly viscousto pasty solution of the alginic acid amide is firstformed, which isthen transformed into a .gel by the action of the acid which 'is'formedin the courseof a certain periodof time. The concentrations to beusedlin this process -are generally less than 30. parts by weight ofgel-forming partial polyuroniea'cid amides per parts by weight of water.It is preferred to work with concentrations between 1 and 5%byweight ofpartial polyur'onic acid amide.

From the group of non-acidic-reacting substances which form acidsgradually in the presence of .water the most interesting from atechnical viewpoint are those which are readily soluble in water both inthe form of the free acidproduced and in the. non-acidic reacting form.For the purpose of the present invention, however, it is suificient ifthe free acids produced are soluble in water to the extent that theyimparta pH-value within therange of 2 to 6 to the gel subsequent to thegel formation. The quantity of non-acidic-reacting substance to be usedshouldbe chosen so that the number of acid groups present after thereaction with water is complete is at least equal .to the number ofneutralized carboxyl groups present in the partial polyuronic acidamides. However, since an excess of non-acidic-reacting substance is notinjurious, the latter can also be used in substantially greaterquantities. In this. case the pH- value which develops subsequent togel'formation and which lies within the above-mentioned range is also agood measure of the quantity of non-acidic-reacting subwith 5 to 100parts by weight of non-acidic-reacting substances per 100 parts byweight of partial polyuronic acid amides.

We have found that firmer gels are obtained when small quantities ofions of polyvalent metals are present. These ions should preferably becolorless ions, such as the ions of calcium, magnesium or aluminum. Thequantityof salts of these ions may be very small and may amount to lessthan 1% by weight based on the partial polyuronic acid amides.Consequently, the small quantities of hardness-forming minerals inordinary tap water are sufiicient to produce the desired effect.

Our invention makes it possible to obtain aqueous gels in the coldwithin relatively short periods of time. Our invention, however, is notlimited to gel formation in the cold as the solution of the gel-formingsubstances can be accelerated by dissolving at elevated temperatures,for example at temperatures up to 100 C. Gel formation is more rapidafter cooling the solution to the gelatinizing temperature, if thegel-forming substances are dissolved in hot water rather than whendissolved in cold water. Moreover, working at elevated temperatures hasthe further advantage that especially homogeneous gels are obtained. Itis often sufficient to obtain the elfects of solution at highertemperatures by using dissolving temperatures of 30 to 50 C.

The substances to be reacted with each other-that is, the partialpolyuronic acid amides and the non-acidicreacting substancesmay beadmixed with each other and may, if desired, be compounded withadditional materials which are to be worked into the gels, and suchcompositions may be stored and sold in commerce.

With the aid of the process according to the present invention,therefore, it is possible to produce gels which are useful for a varietyof scientific, technical and commercial purposes or in the household.Such gels may,

for example, be used in the production of nutrient media formicroorganisms, for pharmaceutical and cosmetic preparations and forother purposes. If the non-acidicreacting substances are physiologicallyharmless materials, the 'composition of our invention may be employed toproduce foods of the gelatin or pudding type, which in contrast to thoseheretofore produced from starch, gelatin, agar-agar, etc.-do not have tobe warmed for preparation. For this purpose the partial polyuronic acidamides may, in addition to the non-acidic-reacting substances necessaryfor the formation of the gel, also containall of the other ingredients,so that ready-to-use dry mixtures which yield appetizing and coherentgelatinlike foods upon stirring the same with a small amount of liquid,such as fruit juices, wine, water or milk can be produced. These foodsmay be consumed in that form or may be further worked up. As an exampleof further treatment, the production of ice cream or similar frozenfoods may be mentioned. In this case it is sufficient if the partialpolyuronic acid amide is used in such low concentrations that the gelsformed thereby are very soft and no longer sufiiciently solid to be cutup. Under these circumstances it is ,possible to Work with partialpolyuronic acid amide concentrations of 0.1 to 5%, preferably 0.2 to 2%,by weight.

The compositions and the process of making'the thermo-reversible aqueousgels in accordance with this invention are specifically illustrated bythe following, nonlimiting examples:

Example I and intimately admixed in a dry state with parts by- 6.5 partsby weight of dry milk powder, 3.7 parts by weight of cocoa, 0.7 part byweight of gluconic acid lactone, 1 part by weight of the alginic acidmentioned in Examples 1 and 5 parts by weight of cane sugar wereintimately mixed. This mixture was stirred into 50 parts by weight ofwater at 55 C. A thin solution was first formed, which upon standing andcooling solidified into a coherent solid gel. This gel was agelatin-like chocolate pudding having an excellent taste.

Example III 0.5 part by weight of gluconic acid lactone, 1 part byweight of the alginic acid amide described in Example I, 0.8 part byweight of vanillin and 5 parts by weight of sugar were mixed and stirredinto 50 parts by weight of cold milk. The mixture was heated to about 70C. The warm mixture was then allowed to stand and cool, whereupon itformed a vanilla pudding having a good taste.

Example IV 20 parts by weight of the alginic acid amide described inExample I were milled and contained no particles having a grain sizeabove 0.09 mm. This fine powder was admixed with 1.5 parts by weight offinely powdered a-dilactone of d-manno-saccharic acid. This mixture wasstirred slowly into 1000 parts by weight of water at 50 C. whilecontinuously stirring, whereupon it rapidly dissolved. The solution wasmaintained at 50 C. for another 20 to 30 minutes and then allowed tocool. A solid, clear, thermo-reversible gel was obtained.

Example V 10 parts by weight of the alginic acid amide described inExample I were mixed in a dry state with 1.2 parts by weight of glycolicacid anhydride. This mixture was stirred into 400 parts by weight ofwater, and the solution was maintained at 60 C. for about 20 minuteswith occasional stirring. Thereafter, the solution was allowed to cool,whereupon it formed a coherent thermoreversible gel.

Example VI 13 parts by weight of the amide of pectic acid, in whichabout 75% of the carboxyl groups originally present has been transformedinto amide groups while the remaining carboxyl groups were present inthe form of ammonium salt groups, were admixed with 1.3 parts by weightof gluconic acid lactone and the mixture was finely milled. Theresulting powder was slowly stirred into 500 parts by weight water at 30C. while continuously stirring. A clear solution was obtained whichbecame more and more solid as it continued to stand, and after about 1hour it solidified into a thermo-reversible gel.

From the foregoing, it will be readily apparent to those skilled in theart that the compositions of this invention can be varied widely withoutlosing the property of obtaining thermo-reversible gels, that is, gelswhich liquify upon heating and solidify again upon cooling.

While we have given specific examples of our new compositions andcertain examples of the process of producing aqueous gels by our method,it will be understood that these examples are for purpose ofillustration and that various modifications and changes can be made inthe examples given without departing from the spirit of our invention orthe scope of the following claims, and that while various theories havebeen given for the purpose of explaining the reactions, we do not intendto be bound by these theories.

We claim:

1. As a composition of matter, a dry mixture capable of forming anaqueous gel when admixed with water, said gel being thermo-reversible,comprising as gel-forming ingredients a water-soluble polyuronic acidamide wherein about 50% to about 80% of the acyl groups are present ascarbonamide groups and the remainder of the acyl groups are presentessentially as neutralized carboxy groups admixed with a sufiicientamount of a watersoluble, non-acidic-reacting organic compound whichforms free acids gradually in the presence of water to impart a pHwithin the range of 2 to 6 to the gel soformed.

2. As a composition of matter, a dry mixture capable of forming anaqueous gel when admixed with water, said gel being thermo-reversible,comprising as gelforming ingredients 100 parts of an alginic acid amidewherein about 50% to about 80% of the acyl groups are present ascarbonamide groups and the remainder of the acyl groups are presentessentially as neutralized carbonxyl groups and 5 to 100 parts of awater-soluble, non-acidic-reacting organic compound which forms freeacids gradually in the presence of water.

3. As a composition of matter, a dry mixture capable of forming anaqueous gel when admixed with water, said gel being thermo-reversible,comprising as gel-forming ingredients 100 parts of a pectic acid amidewherein about 50% to about 80% of the acyl groups are present ascarbonamide groups and the remainder of the acyl groups are presentessentially as neutralized carboxyl groups and 5 to 100 parts of awater-soluble, non-acidicreacting organic compound which forms freeacids gradually in the presence of water.

4. As a composition of matter, a dry mixture capable of forming anaqueous gel when admixed with water, said gel being thermo-reversible,comprising as gel-forming ingredients 100 parts of an alginic acid amidewherein about 70% of the acyl groups are present as carbonamide groupsand the remainder of the acyl groups are present essentially asammonia-neutralized carboxyl groups and 5 to 100 parts of gluconic acidlactone.

5. As a composition of matter, a dry mixture capable of forming anaqueous gel when admixed with water, said gel being thermo-reversible,comprising as gel-forming ingredients 100 parts of an alginic acid amidewherein about 70% of the acyl groups are present as carbonamide groupsand the remainder of the acyl groups are present essentially asammonia-neutralized carboxyl groups and 5 to 100 parts of a-dilactone ofd-mannosaccharic acid.

6. As a composition of matter, a dry mixture capable of forming anaqueous gel when admixed with water, said gel being thermo-reversible,comprising as gel-forming ingredients 100 parts of an alginic acid amidewherein about 70% of the acyl groups are present as carbonamide groupsand the remainder of the acyl groups are present essentially asammonia-neutralized carboxyl groups and 5 to 100 parts of glycolic acidanhydride.

7. As a composition of matter, a dry mixture capable of forming anaqueous gel when admixed with water, said gel being thermo-reversible,comprising as gel-forming ingredients 100 parts of pectic acid amidewherein about 75% of the acyl groups are present as carbonamide groupsand the remainder of the acyl groups are present essentially asammonia-neutralized carboxyl groups and 5 to 100 parts of gluconic acidlactone.

8. A process for the production of thermo-reversible,

aqueous gels comprising dissolving in an excess amount of water asgel-forming ingredients a polyuronic acid amide wherein about 50% toabout of the acyl groups are present as carbonamide groups and theremainder ot the acyl groups are present essentially as neutralizedcarboxyl groups and a sufiicient amount of a Water-soluble,nonacidic-reacting organic compound which forms free acids gradually inthe presence of Water to impart a pH Within the range of 2 to 6 to thegel so-formed and allowing the solution to gel.

9. The process of claim 8 wherein up to about 30 parts of the saidpolyuronic acid amide are used per parts by weight of water.

10. A process for the production of thermo-reversible, aqueous gelscomprising dissolving in an excess amount of water at temperatures offrom about 20 C. to about 100 C. as gel-forming ingredients 100 parts ofan alginic acid amide wherein about 50% to about 80% of the acyl groupsare present as carbonamide groups and the remainder of the acyl groupsare present essentially as neutralized carboxyl groups and 5 to 100parts of a Water-soluble, non-acidic-reacting organic compound whichforms free acids gradually in the presence of water and allowing thesolution to gel.

11. The process of claim 10 wherein said water-soluble,non-acidic-reacting organic compound which forms free acids gradually inthe presence of water is a lactone.

12. The process of claim 10 wherein said water-soluble,non-acidic-reacting organic compound which forms free acids gradually inthe presence of water is an acid anhydride.

13. A process for the production of thermo-reversible, aqueous gelscomprising dissolving in an excess amount of water at temperatures offrom about 20 C. to about 100 C. as gel-forming ingredients 100 parts ofan pectic acid amide wherein about 50% to about 80% of the acyl groupsare present as carbonamide groups and the relmainder of the acyl groupsare present essentially as neutralized carboxyl groups and 5 to 100parts of a watersoluble, non-acidic-reacting organic compound whichforms free acids gradually in the presence of water and allowing thesolution to gel.

14. In the process of making edible puddings and gelatins which requiredissolving gel-forming ingredients in aqueous liquids the improvementwhich comprises utilizing as gel-forming ingredients a polyuronic acidamide wherein about 50% ta about 80% of the acyl groups are present ascarbonamide groups and the remainder of the acyl groups are presentessentially as neutralized carboxyl groups and a sufiicient amount of awater-soluble, nonacidic-reacting organic compound which forms freeacids gradually in the presence of Water to impart a pH within the rangeof 2 to 6 to the gel so-formed.

15. A thermo-reversible aqueous gel comprising water and as gel-formingingredients a polyuronic acid amide wherein about 50% to about 80% ofthe acyl groups are present as carbonamide groups and the remainder ofthe acyl groups are present essentially as neutralized carboxyl groupsand a suflicient amount of a water-soluble, nonacidic-reacting organiccompound which forms free acids gradually in the presence of water toimpart a pH within the range of 2 to 6 to the gel so-formed.

References Cited in the file of this patent UNITED STATES PATENTS Evanset al July 31, 1945 Steiner et al Jan. 17, 1950 OTHER REFERENCES UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noo 2 919 198December 29 1959 R fidolf Kchler et a1.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 4 line 14L for Examples read Example column 45 line 47 for "50%ta" read 50% to Signed and sealed this 23rd day of August 1960."

(SEAL) Attest:

KARL H10 AXLINE 1 ROBERT C. WATSON Attesting Oflicer Commissioner ofPatents

1. AS A COMPOSTION OF MATTER, A DRY MIXTURE CAPABLE OF FORMING ANAQUEOUS GEL WHEN ADMIXED WITH WATER, SAID GEL BEING THERMO-REVERSIBLE,COMPRISING AS GEL-FORMING INGREDIENTS A WATER-SOLUBLE POLYURONIC ACIDAMIDE WHEREIN ABOUT 50% TO ABOUT 80% OF THE ACYL GROUPS ARE PRESENT ASCARBONAMIDE GROUPS AND THE REMAINDER OF THE ACYL GROUPS ARE PRESENTESSENTIALLY AS NEUTRALIZED CARBOXY GROUPS ADMIXED WITH A SUFFICIENTAMOUNT OF A WATERSOLUBLE, NON-ACIDIC-REACTING ORGANIC COMPOUND WHICHFORMS FREE ACIDS GRADUALLY IN THE PRESENCE OF WATER TO IMPART A PHWITHIN THE RANGE OF 2 TO 6 TO THE GEL SOFORMED.